Rationale:
The deprecated support relied on a limited convention that could not be
extended to support the general case or new language features.

It has been
superseded by direct language support with decltype, and by the
std::bind and std::not_­fn function templates.

Effect on original feature:
A valid C++ 2017 program that relies on the presence of result_­type,
argument_­type, first_­argument_­type, or
second_­argument_­type in a standard library class may fail to compile.

A
valid C++ 2017 program that calls not1 or not2, or uses the
class templates unary_­negate or binary_­negate, may fail to
compile.

Rationale:std::allocator was overspecified, encouraging direct usage in user containers
rather than relying on std::allocator_­traits, leading to poor containers.

Effect on original feature:
A valid C++ 2017 program that directly makes use of the pointer,
const_­pointer, reference, const_­reference,
rebind, address, construct, destroy, or
max_­size members of std::allocator, or that directly calls
allocate with an additional hint argument, may fail to compile.

Rationale:
The iterator encouraged use of algorithms that might throw exceptions, but did
not return the number of elements successfully constructed that might need to
be destroyed in order to avoid leaks.

Effect on original feature:
A valid C++ 2017 program that uses this iterator class may fail to compile.

Rationale:
The temporary buffer facility was intended to provide an efficient optimization
for small memory requests, but there is little evidence this was achieved in
practice, while requiring the user to provide their own exception-safe wrappers
to guard use of the facility in many cases.

Effect on original feature:
A valid C++ 2017 program that calls get_­temporary_­buffer or
return_­temporary_­buffer may fail to compile.

Effect on original feature:
A valid C++ 2017 program that relies on the is_­literal_­type or
result_­of type traits, on the is_­literal_­type_­v variable template,
or on the result_­of_­t alias template may fail to compile.